One of the most important interventions for osteoporosis is prevention of bone loss. The main emphasis of prevention strategies has been on dietary calcium intake, however calcium by itself has limited efficacy. Thus, any component that can improve calcium's effect on bone mass can improve bone health significantly. Conjugated linoleic acid (CLA) may be a good candidate for controlling osteoporosis based on the observation that CLA reduces body fat while increasing lean mass along with total ash. However, the reported effects of CLA on bone mass have not been consistent. We hypothesized that the inconsistency of CLA with regard to bone mass is due to differences in dietary calcium content. My long term goal in the original application is to contribute to the development of strategies designed to reduce bone loss through dietary and supplementary based interventions. The objective in the original R21 grant application is to evaluate the extent to which dietary CLA influence bone metabolism with dietary calcium in an experimental osteoporosis model. Based on the original application, we would like to expand our scope of study by adding a new hypothesis that inhibition of adipogenesis by CLA is a significant but not critical contributing factor for CLA's beneficial effects on osteogenesis. The rationale for this revised application is that investigating the role of CLA specifically on balancing adipogenesis and osteogenesis due to the pluripotential nature of mesenchymal stem cells will help understand the critical aspects of CLA in regard to application for eventual use in human health. This revised study will determine if controlling of adipogenesis by CLA is critical for CLA's impact on bone health. Thus, the research in the requested revision is relevant to that part of NIH's mission that pertains to developing knowledge that will potentially help to reduce human diseases. The new hypotheses will be tested by pursuing a new Specific Aim: (3) Determine the role of CLA in the balance between osteogenesis and adipogenesis in bone marrow mesenchymal stem cells. By using mesenchymal stem cells knocked-down for target mediators of osteogenesis and adipogenesis, we will focus on identifying the role of CLA on adipogenesis that can directly influence osteogenesis or vice versa. The scope of the overall project is to investigate the underlying role of CLA on bone mass improvement, which may lead to the application ofCLA as a dietary supplement or food additive for prevention of bone loss. The anticipated contribution of the requested revision is that the revised application will contribute to comprehensively integrate and expand new insight for understanding the interrelationship between osteoblasts and adipocytes from mesenchymal stem cells as well as the potential use of CLA to prevent osteoporosis. The Public Health relevance of this project is that identifying any dietary components that can improve bone health will have a significant impact on reduction and/or prevention of osteoporosis, which can lead to an improved quality of life, particularly in the elderly. PUBLIC HEALTH RELEVANCE: Osteoporosis is a disease characterized by low bone mass, with the elderly particularly susceptible, and it affects the quality of life as well as increasing mortality, due to complications. A unique prevention strategy by controlling balance of bone formation and fat cell formation from bone marrow stem cell by conjugated linoleic acid can potentially be a very useful tool for preventing the development of osteoporosis, leading to improved quality of life particularly in the elderly.